The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is driven by several turbojet engines, each housed in a nacelle also hosting an assembly of auxiliary actuating devices linked to its operation and providing various functions when the turbojet engine is operating or stopped. These auxiliary actuating devices comprise, in particular, a mechanical thrust reverser device.
The propulsion assembly of the aircraft formed by the nacelle and the turbojet engine is intended to be hung to a fixed structure of the aircraft, for example under a wing or on the fuselage, via a suspension pylon.
The nacelle generally has a tubular structure comprising an air inlet upstream of the turbojet engine, a median section intended to surround a fan of the turbojet engine, a downstream section hosting the thrust reverser means and intended to surround a combustion chamber and the turbojet engine turbines, and is generally terminated by an exhaust nozzle of which the outlet is located downstream of the turbojet engine.
This nacelle can be intended to host a turbofan engine, namely a turbojet engine capable of generating a hot air flow (also called primary flow) coming from the combustion chamber of the turbojet engine, and via the rotating fan blades and a cold air flow (secondary flow) which flows outside the turbojet engine through a flow stream of the cold air flow.
An outer structure called OFS (Outer Fan Structure), hosting the thrust reverser means, and an inner structure, called IFS (Inner Fan Structure), which surrounds the engine structure on itself behind the fan, intended to cover a downstream section of the turbojet engine, both belonging to the downstream section of the nacelle, define the flow stream of the cold air flow and thus a passage section of the cold air flow.
Regarding the thrust reverser device, it is adapted, during landing of the aircraft, to improve the braking capacity thereof by redirecting forward at least one part of the thrust generated by the turbojet engine.
During this phase, it obstructs the flow stream of the cold air flow and directs the latter towards the front of the nacelle, thereby generating a counter-thrust which adds to the braking of the aircraft wheels.
FIGS. 1 to 4 show a known example of a form of a thrust reverser.
This thrust reverser 10 is composed of a fixed structure (a front frame 12, a cascade 11, a rear frame 13 and the IFS 17) and a movable structure.
More specifically, this thrust reverser 10 includes a plurality of diversion cascade 11, attached between the peripheral front frame 12 and the fixed peripheral rear frame 13 which, generally, joins together an outer panel 14 and an inner panel 15 of a movable thrust reverser cowl 16.
During operation, the reorientation of the secondary flow, in the reverse jet position, is performed by this diversion cascade 11, the movable cowl 16 having primarily a sliding function aiming to uncover or cover this diversion cascade 11, the translation of the movable cowl 16 being performed along a longitudinal axis substantially parallel to a central axis A of the turbojet engine.
Complementary blocking doors, also called flaps 18, activated by the sliding of the cowl 16, allow a closing of the flow stream 19 of the secondary flow, downstream the cascade 11 so as to allow the reorientation of the secondary flow towards the diversion cascade 11.
These flaps 18 are pivotally mounted on the cowl 16 sliding between a retracted position in which they provide, with said movable cowl 16, the aerodynamic continuity of the inner wall of the cowl 16 and a deployed position in which, in a thrust reversal situation, they obstruct at least partially the stream 19 in order to divert the secondary flow towards the diversion cascade 11 uncovered by the sliding of the cowl 16.
This thrust reverser 10 is conventionally mounted on a nacelle substantially of revolution around the central axis A of the turbojet engine.
The aerodynamic lines of the nacelle allow a mounting of identical diversion cascade 11 on the entire circumference of the stream 19.
More particularly, as illustrated in FIGS. 2, 3 and 4, the mounting of the cascade 11 is centered on the central axis A of the turbojet engine on the entire circumference of the stream 19.
More specifically, the connecting interface 20 between the front frame and the upstream end of each cascade is radially centered on the axis A just as the connecting interface 21 between the rear frame 13 and the downstream end of each cascade 11.
Thus, the radius R1 of the connecting interface 20 between the front frame 12 and the upstream end of each cascade 11 is constant for all the cascade 11 connections on the front frame 12 on the entire circumference of the stream 19, just as the radius R3 of the connecting interface 21 between the rear frame 13 and the downstream end of each cascade 11.
Moreover, as illustrated in FIGS. 3 and 4, the radius R2 of the flow diversion blades of the diversion cascade 11 defined as the radius of the inner face of each cascade 11 from the stream 19 side, is also constant on the entire periphery of the flow exhaust stream 19.
The installation of such a cascade-type thrust reverser device 10 on a turbojet engine under the airfoil becomes complicated when the maximum height constraint of the nacelle is critical due to a low ground clearance of the aircraft and proximity between the turbojet engine and the aircraft airfoil.
Such an installation further involves a sensitive management of the passage section of the cold air flow.
A reduction of the nacelle height has therefore been proposed by providing a nacelle of non revolution around the central axis A of the turbojet engine, called “flattened nacelle”.
Such a flattened nacelle has reduced aerodynamic lines in the areas at twelve hour position (i.e. in the upper part of the nacelle) and at six hour position (i.e. in the lower part of the nacelle).
Such a nacelle has no impact on the effectiveness of the thrust reversal.
However, in this case, it is necessary to locally arrange the flow diversion cascade 11.
The mounting of the flow diversion cascade 11 is achieved by reducing the radius R2 of the blades of the diversion cascade 11, which, consequently, is no longer constant over the entire periphery of the stream 19.
This involves the use of diversion cascade 11 especially dedicated to areas of the reduced aerodynamic lines of the nacelle to adjust with the height of the stream or the cowl which is different at twelve hour position (i.e. in the upper part of the nacelle) and at six hour position (i.e. in the lower part of the nacelle).
The diversion cascade 11 mounted in the areas of reduced aerodynamic lines of the nacelle are therefore not interchangeable anymore with the other diversion cascade intended to be placed on the remainder of the periphery of the stream.
The manufacturing costs are multiplied due to the multiplication of the diversion cascade categories to be provided for, the associated molds and manufacturing lines as well as maintenance costs.